Contactless system and method for assessing tissue viability and other hemodynamic parameters

ABSTRACT

A contactless system for assessing tissue viability and other hemodynamic parameters includes one or more light sources configured to emit lights at a predetermined wavelength sensitive to hemoglobin concentration associated with spontaneous hemodynamic oscillations at tissue in a predetermined area of a human subject. One or more polarizers are each coupled to one or more of the one or more light sources and are configured to polarize the light to a polarized state such that the polarized light in the polarized state diffuses into the tissue in the predetermined area at a predetermined depth and the polarized light is maintained in the polarized state at the predetermined depth. One or more detectors each including a detector polarizer coupled thereto are configured to discriminate the light maintained in the polarized state and at the predetermined depth and are configured to generate a plurality of frames of the tissue in the predetermined area at the predetermined depth. A controller is coupled to the one or more light sources and the one or more detectors. The controller is configured to: acquire the plurality of frames, select a region of interest having the same coordinates for each of the plurality of frames, average the number of pixels within each region of interest to create a raw reference signal, detrend the raw reference signal to create a detrended raw reference signal, perform frequency domain analysis of the detrended raw reference signal, identify a frequency band of interest associated with the spontaneous hemodynamic oscillations, and perform an inverse fast Fourier transform within the frequency band of interest to generate a reference signal indicative of blood volume oscillations at a selected spontaneous hemodynamic oscillation. For each sample of the reference signal at a predetermined point in time, the controller multiplies the sample by each pixel of a frame at the same predetermined point in time to generate a three-dimensional coordinate matrix including a plurality of correlation matrix frames at each predetermined point in time. The controller adds the plurality of correlation matrix frames at each predetermined point in time to generate a two-dimensional hemodynamic map indicative of the strength of the spontaneous hemodynamic oscillation to assess the viability of the tissue in the predetermined area.

RELATED APPLICATIONS

This application is a reissue application of U.S. Pat. No. 10,448,835issued Oct. 22, 2019, which patent hereby claims the benefit of andpriority to U.S. Provisional Patent Application Ser. No. 62/621,873filed Jan. 25, 2018, under 35 U.S.C. §§ 119, 120, 363, 365, and 37C.F.R. § 1.55 and § 1.78, which is incorporated herein by thisreference.

GOVERNMENT RIGHTS

This invention was made with government support under contract numberW81XWH-17-C-0169, awarded by the Department of Defense. The governmenthas certain rights in the invention.

FIELD OF THE INVENTION

This invention relates to a contactless system and method for assessingtissue viability and other hemodynamic parameters.

BACKGROUND OF THE INVENTION

Burn wounds may be classified into four categories of increasing depth:superficial, intermediate partial thickness, deep partial thickness, andfull thickness. The latter two classifications typically requireaggressive interventions that involve the debridement of necrotic tissueand the application of split thickness skin grafts. These are moremorbid wounds typically wrought with the potential for hypertrophicscarring and contractures and may necessitate early surgical excisionand grafting to optimize the outcome, See e.g., Ryan et al., ObjectiveEstimates of the Probability of Death From Burn Injuries, N. Engl. J.Med., 1998, 338: 362-6, incorporated by reference herein. Selecting thelevel of debridement sufficient to minimize inflammation and determiningthe optimal treatment in a timely fashion is critical given the risks ofinfection and sepsis. The success of grafting depends on the removal ofvirtually all necrotic tissue and any biofilm and requires the presenceof highly-vascularized granulation tissue. The goal of early debridementfor grafting is to remove all the devitalized tissue for skin graftinguntil only granulation tissue remains. Using a conventional tissueexcision procedure, several layers of burned tissue are excised untilthe viable wound bed is reached, as evidenced by capillary bleeding. Seee.g., Orgill et al., Excision and Skin Grating Of Thermal Burns, NewEngland Journal of Medicine, 2009, Feb. 26; 360(9): 893-901,incorporated by reference herein. Although bleeding is typically assumedto mean the tissue is viable, this conventional tissue excisionprocedure is subjective and imprecise because it relies on visualinspection that does not preclude the possibility that some necrotictissue or biofilm will be inadvertently left in the wound site.

Given the challenges in objectively determining tissue viability, anumber of conventional technologies have been repurposed with the intentof providing metrics of tissue viability, such as Laser Doppler Imaging(LDI) and Indocyanine green angiography (ICG).

Conventional LDI is a highly recognized noninvasive technique forclinical evaluation of burn wound and tissue viability assessment.Several conventional LDI devices are available which estimate the bloodflow in the area of interest. See e.g., Jaskille et al., Critical Reviewof Burn Depth Assessment Techniques: Part II, Review of Laser DopplerTechnology, Journal of Burn Care & Research, 2010, Jan. 1; 31(1):151-7,incorporated by reference herein. However, LDI has several drawbacks.Because flowmetry requires the probe to directly contact with the burnwound, it may increase the risk of wound infection and may inflicttrauma to already vulnerable tissue. See e.g., O'Reilly et al., LaserDoppler Flowmetry Evaluation of Burn Wound Depth, Journal of Burn Care &Research, 1989, Jan. 1; 10(1):1, incorporated by reference herein.Additionally, because LDI measures perfusion in one spot at the time,assessing a large burn wound may be a time-consuming process.Additionally, there is some risk that LDI may not detect necrotic tissuein the wound bed. See e.g., Atiles et al., Laser Doppler Flowmetry InBurn Wounds, Journal of Burn Care & Research, 1995, Jul. 1; 16(4):388-93, incorporated by reference herein.

Conventional Indocyanine green (ICG) video-angiography provides greaterskin imaging penetration compared to LDI. ICG enables visualization ofthe deep dermal vasculature using a dye. See e.g., Jerath et al., BurnWound Assessment in Porcine Skin Using Indocyanine Green Fluorescence,Journal of Trauma and Acute Care Surgery, 1999, Jun. 1; 46(6): 1085-8,incorporated by reference herein. ICG is based on the fluorescentproperties of the dye being used and quantifying the intensity of thedye. ICG provides color-coded maps relative to the perfusion of theinvestigated area. The major drawback associated with conventional ICGvideo-angiography is that intravascular dye injection is required.Previous studies have shown a high degree of association betweenheadache, pruritus, urticarial and anaphylactic reaction following thedye injection. See e.g., Benya et al., Adverse Reactions to IndocyanineGreen: A Case Report and a Review of the Literature. Catheterization andCardiovascular Diagnosis, 1989, Aug. 1; 17(4):231-3, incorporated byreference herein.

While conventional LDI and ICG each offer a unique approach to detectingtissue viability, both techniques are cumbersome to manipulate in asurgical setting, have a large size, and do not provide for real-timediagnosis, critical for tissue viability assessment during an excisionprocedure.

SUMMARY OF THE INVENTION

In one aspect, a contactless system for assessing tissue viability andother hemodynamic parameters is featured. The system includes one ormore light sources configured to emit lights at a predeterminedwavelength sensitive to hemoglobin concentration associated withspontaneous hemodynamic oscillations at tissue in a predetermined areaof a human subject. One or more polarizers each coupled to one or moreof the one or more light sources are configured to polarize the light toa polarized state such that the polarized light in the polarized statediffuses into the tissue in the predetermined area at a predetermineddepth and the polarized light is maintained in the polarized state atthe predetermined depth. One or more detectors each including a detectorpolarizer coupled thereto are configured to discriminate the lightmaintained in the polarized state and at the predetermined depth andconfigured to generate a plurality of frames of the tissue in thepredetermined area at the predetermined depth. A controller is coupledto the one or more light sources and the one or more detectors and isconfigured to: acquire the plurality of frames, select a region ofinterest having the same coordinates for each of the plurality offrames, average the number of pixels within each region of interest tocreate a raw reference signal, detrend the raw reference signal tocreate a detrended raw reference signal, perform frequency domainanalysis of the detrended raw reference signal, identify a frequencyband of interest associated with the spontaneous hemodynamicoscillations, perform an inverse fast Fourier transform within thefrequency band of interest to generate a reference signal indicative ofblood volume oscillations at a selected spontaneous hemodynamicoscillation, for each sample of the reference signal at a predeterminedpoint in time, multiply the sample by each pixel of a frame at the samepredetermined point in time to generate a three-dimensional coordinatematrix including a plurality of correlation matrix frames at eachpredetermined point in time, and add the plurality of correlation matrixframes at each predetermined point in time to generate a two-dimensionalhemodynamic map indicative of the strength of the spontaneoushemodynamic oscillation to assess the viability of the tissue in thepredetermined area.

In one embodiment, the spontaneous hemodynamic oscillations may have afrequency in the range of 0.05 Hz to about 1.5 Hz. The predeterminedwavelength may be in the range of about 500 nm to about 1,000 nm. Thepredetermined depth may be in the range of about 0.1 mm to about 0.5 mm.The other hemodynamic parameters may include one or more of: heart rate,resting heart rate, heart rate variability, and tissue saturation forpatients suffering from diminished blood circulation, and other similartype hemodynamic parameters. The one or more detectors may include a CCDcamera. The one or more detectors may include a CMOS camera. Thepredetermined area may include a burn area of the human subject. Thepredetermined area may include a wound area of a human subject. Thesystem may include a light filtering lens coupled to one or more lightsources.

In another aspect, a contactless method for assessing tissue viabilityand other hemodynamic parameters is featured. The method includesemitting light at a predetermined wavelength sensitive to hemoglobinconcentration associated with spontaneous hemodynamic oscillations attissue in a predetermined area of a human subject. The light ispolarized to a polarized state such that the polarized light in thepolarized state diffuses into the tissue in the predetermined area at apredetermined depth and the polarized light is maintained in thepolarized state at the polarized depth. The light maintained in thepolarized state and at the predetermined depth is discriminated. Aplurality of frames of the tissue in the predetermined area at thepredetermined depth are generated and acquired. A region of interest isselected having the same coordinates for each of the plurality offrames. The number of pixels within each region of interest is averagedto create a raw reference signal. The raw reference signal is detrendedto create a detrended raw reference signal. A frequency domain analysisof the detrended raw reference signal is performed. A frequency band ofinterest associated with the spontaneous hemodynamic oscillations isidentified. An inverse fast Fourier transform within the frequency bandof interest is performed to generate a reference signal indicative ofblood volume oscillations at a selected spontaneous hemodynamicoscillation. For each sample of the reference signal at a predeterminedpoint in time, the sample is multiplied by each pixel of a frame at thesame predetermined point in time to generate a three-dimensionalcoordinate matrix including a plurality of correlation matrix frames ateach predetermined point in time. The plurality of correlation matrixframes at each predetermined point in time are added to generate atwo-dimensional hemodynamic map indicative of the strength of thespontaneous hemodynamic oscillation to assess the viability of thetissue in the predetermined area.

In one embodiment, the plurality of correlation matrix frames at eachpredetermined point in time are added to generate a two-dimensionalhemodynamic map indicative of the strength of the spontaneoushemodynamic oscillation to assess the viability of other hemodynamicparameters including one or more of: heart rate, resting heart rate,heart rate variability, and tissue saturation for patients sufferingfrom diminished blood circulation and similar type hemodynamicparameters. The spontaneous hemodynamic oscillations may have afrequency in the range of 0.05 Hz to about 1.5 Hz. The predeterminedwavelength may be in the range of about 500 nm to about 1,000 nm. Thepredetermined depth may be in the range of about 0.1 mm to about 0.5 mm.The predetermined area may include a burn area of the human subject. Thepredetermined area may include a wound area of a human subject.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic diagram showing the primary components of oneembodiment of the contactless system and method for assessing tissueviability and other hemodynamic parameters;

FIG. 2 is a schematic diagram showing in further detail the interactionof polarized light in a polarized state with tissue in the predeterminedarea shown in FIG. 1 ;

FIG. 3 depicts graphs of various types of polarized light which may beprovided by the polarizer coupled to the one or more light sources shownin FIG. 1 ;

FIG. 4 is a block diagram showing one example of the primary stepsperformed by the controller shown in FIG. 1 to create a hemodynamic mapto assess tissue viability and other hemodynamic parameters;

FIG. 5 is a schematic block diagram showing in further detail oneexample of the step of creating the hemodynamic map shown in FIG. 4 ;and

FIG. 6 is a schematic block diagram showing one example of the primarysteps of one embodiment of the contactless method for assessing tissueviability and other hemodynamic parameters.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

FIG. 1 shows one embodiment of contactless system 10 for assessing oftissue viability and other hemodynamic parameters. System 10 preferablyincludes one or more light sources 12 configured to emit light 14 at apredetermined wavelength sensitive to hemoglobin concentrationassociated with spontaneous hemodynamic oscillations at tissue 16 inpredetermined area 18 of a human subject 20 having a burn wound orsimilar type wound where the tissue viability of human subject 20 needsto be determined, as discussed in the Background section above. Tissue16 in predetermined area 18 may be any tissue in any area on humansubject 20 having a burn wound or similar type wound, e.g., such asdiabetic ulcers or similar type wounds. In the example shown in FIG. 1 ,predetermined area 18 is located on the face, neck, and upper chest ofhuman subject 20. In other examples, predetermined area 18 may be anyarea of the human subject 20 having a burn wound or similar type woundwhere tissue viability needs to be determined. One or more light sources12 are preferably placed above and proximate tissue 16 in predeterminedarea 18 and emit or illuminate light 14 having one or more wavelengthssensitive to hemoglobin concentration spontaneous oscillations andcapable of probing the human tissue without being completely absorbed,as discussed in further detail below. In one example, one or more lightsources 12 preferably emit or illuminate light 14 having wavelengths inan electromagnetic (EM) spectrum, e.g., in the range of about 500 nm toabout 1000 nm. In one example, the spontaneous hemodynamic oscillations,e.g., cardiac and respiratory induced oscillations, have a frequency inthe range of about 0.05 Hz to about 1.5 Hz associated with blood volumechanges. In one design, one or more light sources 12 may include nearinfrared (NIR) sensors and/or one or more near infrared spectroscopy(NIRS) sensors.

System 10 also includes one or more polarizers each coupled to one ormore light sources. FIG. 2 shows an example of polarizer 22 coupled tolight source 12. Each of the one or more light sources 12 shown in FIG.1 similarly has polarizer 22 coupled thereto. Each polarizer 22, FIG. 2, coupled to light source 12 is configured to polarize light 14 topolarized light 14 ^(p) in a polarized state such that polarized light14 ^(p) in the polarized state diffuses into tissue 16 in predeterminedarea 18 and polarized light 14 ^(p) is maintained in the polarized stateat predetermined depth d-24. In one example, depth d-24 is in the rangeof about 0.1 mm to about 0.5 mm. For example, when polarized light 14^(p) is incident on tissue 16 in predetermined area 18, some of thephotons polarized light 14 ^(p) will reflect off the surface of tissue16 and some photons will penetrate into tissue 16 where the photons willeither be scattered or absorbed as shown. If light polarized 14 ^(p)incident light is reflected off the surface of the tissue 16, e.g.,indicated at 26, the polarization state is perfectly maintained.However, the polarization state of the penetrating photons of polarizedlight 14 ^(p) may be affected by scattering events in tissue 16 whichmay be divided into two categories: polarization maintaining ordepolarized. If the photons do not travel deep into the tissue of tissue16 only a limited number of scattering events will occur and thepolarization is maintained, but some alterations have likely occurred.However, if photons travel deeper into tissue 16 and more scatteringevents occur, the polarization of polarized light 14 ^(p) becomesincreasingly depolarized. Therefore, by utilizing one or more polarizer22 each coupled to one or more light sources 12, the degree ofpolarization can be maintained to discriminate the depth of penetrationof light into the tissue of tissue 16, e.g., polarized light 14 ^(pd) atdepth d-24, e.g., is about 0.1 mm to about 0.5 mm. Such a depth istypically needed for real-time assessment of tissue viability of tissue16 in predetermined area 18 by clinicians in an objective manner, asdiscussed below.

Polarized light 14 ^(p) emitted from each polarizer 22 provides arelatively low-cost solution to enable real-time assessment of thetissue viability and other hemodynamic parameters of tissue 16 inpredetermined area 18. As polarized light 14 ^(p) transverselypropagates through time and space, it contains both oscillatingorthogonal electric and magnetic field vectors. The polarization ofpolarized light 14 ^(p) as disclosed herein refers to the direction andmanipulation of the oscillating electric field vector. Polarization maybe produced and manipulated by polarizer 22 coupled to one or more lightsources 12. Polarizer 22 may be placed in any desired position alongpath of light 14 from detectors 12, FIGS. 1 and 2 , to tissue 16 inpredetermined area 18. Polarized light 14 provided by one or more lightsources 12 and polarizer 22 coupled thereto may include linearlypolarized light 14′, FIG. 3 , circular polarized 14″ or ellipticalpolarized light 14′″, depending on the arrangement of the opticalcomponents used. Linearly polarized light 14′ may be produced when asingle electric field oscillation plane is isolated using polarizer 22configured as linear polarizer, where one oscillation plane is dictatedby the polarizing axis. The resulting electric field vector isconsidered to oscillate in one plane in which the orthogonal Ex-30 andEy-32 components are maintained the same phase and amplitude as shown.Circularly polarized light 14″ may be provided by polarizer 22 coupledto one or more light sources 12 when one of the two Ex-30 and Ey-32components of the linearly polarized electric field vector becoming outof phase by exactly ±90 from the other as shown. Circularly polarizedlight 14″ may be provided by polarizer 22 coupled to one or more lightsources 12 when polarizer 22 is configured as a quarter-wave platerotated 45 degrees relative to the polarizing axis of the linearpolarizer. As circularly polarized light propagates through time, theshape of the propagation may be considered as a helix rotating eitherclockwise or counter-clockwise, which is denoted as right-handed orleft-handed respectively. Elliptically polarized light 14′″ is providedby polarizer 22 coupled to one or more light sources 12 when linearlypolarized light passing through polarizer 22 is configured as a waveplate or birefringent material where the electric field vectorcomponents become out of phase by any amount other than ±90 degrees.Polarized light 14′, polarized light 14″ or polarized light 14′″provided by polarizer 36 coupled to one or more light sources 12 underthese different polarization states will respond differently whenfocused on a turbid media, such as tissue 16, FIG. 1 , of human subject20 in predetermined area 18.

In the example discussed above with reference to FIG. 2 , polarizedlight 14 ^(p) and polarized light 14 ^(pd) may be one or more ofpolarized light 14′, 14″, and/or 14′″, FIG. 3 .

System 10 may also include one or more light filtering lenses coupled toone or more light sources 12, e.g., light filtering lens 46 showncoupled to polarizer 22. Light filtering lens 46 is preferablyconfigured to be transmissive within the desired operating spectrumdiscussed above and configured to block EM waves outside of the desiredspectrum.

System 10 also includes one or more detectors 40, FIGS. 1 and 2 , whicheach include detector polarizer 42, FIG. 2 , coupled thereto. In oneexample, one or more detectors 40 preferably include one or morehigh-quality CCD cameras, one or more CMOS cameras, or similar typedetectors. One or more detectors 40 may each include sensors having ananalog amplifier and filter configured to increase the gain on thesignal and reduces background noise to create clean images.

Each of detector polarizer 42 are configured to discriminate betweenpolarized light 14 ^(pd) maintained in the polarized state and at thepredetermined depth, d-24, in from tissue 16 and polarized light 14 ^(p)reflected from tissue 16 which has not been maintained in the polarizedstate and at the predetermined depth. For example, as shown generally byarrow 43, each detector polarizer 42 coupled to detector 40discriminates between polarized light 14 ^(pd) that has been maintainedin the polarized state at predetermined depth, d-24, in tissue 16 andpolarized light 14 ^(p) which has not been maintained in the polarizedstate at predetermined depth, d-24.

One or more detectors 40, FIGS. 1 and 2 , e.g., one or more CCD camerasor CMOS cameras, or similar type devices, are configured to generate aplurality of frames of tissue 16, FIGS. 1 and 2 , in predetermined area18 from discriminated polarized light 14 ^(pd) reflected from tissue 16in predetermined area 18 at predetermined depth, d-24, FIG. 2 , e.g.,plurality of frames 40, FIG. 4 , at different points in time rangingfrom, t₁, t₂, t₃ . . . t_(N).

System 10 also includes controller 50, FIGS. 1 and 2 , coupled to one ormore light sources 12 and one or more detectors 40. Controller 50 may bea processor, one or more processors, an application-specific integratedcircuit (ASIC), firmware, hardware, and/or software (including firmware,resident software, micro-code, and the like) or a combination of bothhardware and software that may all generally be referred to herein as a“controller”, which may be part of contactless system 10 and methodthereof for assessing tissue viability and other hemodynamic parameters.Computer program code for the programs for carrying out the instructionsor operation of controller 50 may be written in any combination of oneor more programming languages, including an object oriented programminglanguage, e.g., C++, Smalltalk, Java, and the like, or conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages.

Controller 50 acquires the plurality of frames 40, FIG. 4 , to provideimage acquisition, preferably at a high rate, e.g., greater than about 5frames per second (fps). Controller 50 then selects a region of interest(ROI) having the same coordinate for each of the plurality of frames.For example, ROI-52, which includes pixels from i=1 to i=N as shown, isselected by controller 50 from frame 44 at point t₁. Similarly,controller 50 selects a ROI-52 having the same pixel coordinates foreach of the plurality of frame 44 at points of time, t₁, t₂, t₃ . . .t_(N).

Controller 50 then averages the number of pixels from i=I to i=n withineach ROI-52 of each of the plurality of frames 40, at times t₁, t₂, t₃ .. . t_(N), indicated at 54, to create raw reference signal 56. In oneexample, controller 50 uses equation (1) below to averages the number ofpixels within each ROI-52:

$\begin{matrix}{\sum\limits_{N}{\sum{\frac{1}{n}{ROI}_{NPIXELS}}}} & (1)\end{matrix}$where n is the number of pixels in the selected ROI and N is the numberof acquired frames.

Controller 50 then detrends raw reference signal 56, indicated at 58, tocreate detrended raw reference signal 60.

Controller 50 then performs frequency domain analysis of detrended rawreference signal 60 and identifies a frequency band of interestassociated with the spontaneous hemodynamic oscillations. In thisexample, controller 50 has identified the frequency band of interestbetween F₁-62 and F₂-64 associated with spontaneous hemodynamicoscillations 66. The frequency band of interest associated with thespontaneous hemodynamic oscillations is typically in the range of 0.05Hz to about 1.0 Hz, as discussed above.

Controller 50 then performs inverse fast Fourier transform (iFFT),indicated at 68, within the frequency band of interest, F₁-62 to F₂-64,to generate reference signal (R_(s)) 70 indicative of blood volumeoscillations at selected hemodynamic oscillations.

For each sample of reference signal 70 at a predetermined point in time,controller 50 multiplies the sample by each pixel of a frame at the samepredetermined point in time to generate three-dimensional correlationmatrix 72 which includes a plurality of correlation matrix frames 74 ateach predetermined point in time. As discussed above, each of theplurality of frames 40 is acquired at a various point of time, e.g.,time ranging from t₁, t₂, t₃, . . . t_(N). Reference signal 70, shown ingreater detail in FIG. 5 , includes the same number of samples as thenumber of plurality of frames 40, FIG. 4 , e.g., sample-80, FIG. 5 , attime t₁, sample 82 at time t₂, sample 84 at time t₃ and sample 86 attime t_(N). Controller 50 multiplies each sample by each pixel of eachof the plurality of frames 40 to generate correlation matrix 72 with aplurality of correlation matrix frames 74. In this example, sample 80 attime t₁ is shown being multiplied each of the pixels ranging from i=1 toi=n of frame 44 at the same time t₁, as indicated by lines 90.Similarly, sample 88 at time t_(N) is shown being multiplied each of thepixels ranging from i=1 to i=n of frame 44 at the same time t_(N). Thesame is done for all of the samples at each point in time.

In one example, correlation matrix 72 is generated using equation (2):FRAME_(i)*R_(Si)  (2)where FRAME_(i) is each individual pixels in specific frame at time i,e.g., t₁, t₂, t₃, . . . t_(N), and R_(Si) is a sample at time i of theReference Signal, e.g., t₁, t₂, t₃, . . . t_(N).

Controller 50 then adds the plurality of correlation matrix frames 74 ateach predetermined point in time to generate two-dimensional hemodynamicmap 100, FIG. 4 , indicative of the strength of spontaneous hemodynamicoscillations to assess the viability of tissue 16 in predetermined area18. In one example, equation (3) below is used to generatetwo-dimensional hemodynamic map 100:

$\begin{matrix}{\sum_{i = 1}^{N}{CMx}} & (3)\end{matrix}$where i is correlation matrix at time, i, e.g., t₁, t₂, t₃, . . . t_(N).N is the total amount of is acquired frames, and CMx is the hemodynamicmap showing areas of viable tissue.

In one design, system 10, FIG. 1 , preferably includes display device102 coupled electronically or wirelessly to controller 50, e.g., acomputer monitor, a smart phone, a tablet, or similarly type device,which displays two-dimensional hemodynamic map 100.

The result is system 10 provides hemodynamic map 100, FIGS. 1 and 2 , oftissue 16 in predetermined area 18 and at a depth of about 0.1 mm toabout 0.5 mm needed for real-time assessment of the viability of tissue16 in predetermined area 18 or other hemodynamic parameters, e.g., heartrate, resting heart rate, heart rate variability, tissue saturation forpatients suffering from diminished blood circulation, and the like. Inone design, system 10 provides hemodynamic map 100 which shows viableand necrotic tissue areas. If hemodynamic oscillations are detected andshown on hemodynamic map 100, e.g. indicated at 106 in caption 108, orshown in FIG. 4 , the tissue is viable. If hemodynamic oscillations arenot shown, and therefore not detected by the procedure described above,on hemodynamic map 100, the tissue is necrotic, e.g., indicated at 108,FIGS. 1 and 4 .

Hemodynamic map 100, FIGS. 2 and 4 , preferably has a maximum field ofview (FOV) of tissue 16 in predetermined area 18 where tissue viabilityneeds to be determined. In one design, the FOV, e.g., FOV-104, FIG. 1 ,displayed on display device 102 provides a real-time view of tissue 16in predetermined area 18 needed for real-time assessment of tissueviability in an objective manner. In one example, FOV-104 of tissue 16in predetermined area 18 may be about 10 inches by 10 inches. In otherexamples, FOV-104 of tissue 16 in predetermined area 18 may be larger orsmaller than 10 inches by 10 inches as needed.

Controller 50, FIGS. 1 and 2 , is also preferably configured to storedata associated with one or more hemodynamic maps 100 created bycontroller 100 in storage device 110. Storage device 110 may include anycombination of computer-readable media or memory. The computer-readablemedia or memory may be a computer-readable signal medium or acomputer-readable storage medium. A computer-readable storage medium ormemory may be, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. Other examples may include an electricalconnection having one or more wires, a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), anoptical fiber, a portable compact disc read-only memory (CD-ROM), anoptical storage device, a magnetic storage device, or any suitablecombination of the foregoing. As disclosed herein, the computer-readablestorage medium or memory may be any tangible medium that can contain, orstore one or more programs for use by or in connection with one or moreprocessors on a computing device such as a computer, a tablet, a cellphone, a smart device, or similar type device. Controller 50 may also beconfigured to compress the data associated with the hemodynamic maps.

To reduce and minimize the impact of uncontrolled ambient light changes,system 10 and the method thereof may implement spectral estimationtechniques of the ambient illumination to remove uncontrolled ambientlight changes. In other designs, system 10 and the method thereof mayremove ambient lighting artifacts at the acquisition level by removingtemporal changes in ambient illumination measured during programmedperiods of non-active tissue illumination.

System 10 also preferably includes user interface 112 coupled tocontroller 50 electronically or wirelessly which may allow a user ofsystem 10 to visualize and interact with the stored or real-time data.Data may be retrieved from controller 50 and storage device 110 via adata jack or by wireless communication, as known by those skilled in theart. System 10 also includes power supply 116 configured to providepower to one or more light sources 12, one or more detectors 20,controller 50, and/or display device 102. In one design, power supply116 may include batteries for portable applications.

In other designs, contactless system 10 and method for assessing tissueviability and other hemodynamic parameters may be a standalone devicefor operation room, a portable device, or integrated into wearable toolswore by medical personnel.

One example of the method for assessing tissue viability and otherhemodynamic parameters includes emitting light at a predeterminedwavelength sensitive to hemoglobin concentration associated withspontaneous hemodynamic oscillations at tissue in a predetermined areaof a human subject, step 150, FIG. 6 . The method also includespolarizing the light to a polarized state such that the polarized lightin the polarized state diffuses into the tissue in the predeterminedarea at a predetermined depth such that the polarized light ismaintained in the polarized state at the polarized depth, step 152. Themethod also includes discriminating the light maintained in thepolarized state and at the predetermined depth and generating aplurality of frames of the tissue in the predetermined area at thepredetermined depth, step 154. A plurality of frames are then acquired,step 156. A region of interest is then selected having the samecoordinates for each of the plurality of frames, step 158. The number ofpixels within each region of interest is averaged to create a rawreference signal, step 160. The raw reference signal is detrended tocreate a detrended raw reference signal, step 162. Frequency domainanalysis is performed of the detrended raw reference signal, step 168. Afrequency band of interest is identified associated with the spontaneoushemodynamic oscillations, step 170. An inverse fast Fourier transform(iFFT) is performed within the frequency band of interest to generate araw reference signal indicative of blood volume oscillations at aselected spontaneous hemodynamic oscillation, step 172. For each sampleof the raw reference signal at a predetermined point in time, the sampleis multiplied by each pixel of a frame at the same predetermined pointin time to generate a three-dimensional coordinate matrix including aplurality of correlation matrix frames at each predetermined point intime, step 174. The plurality of correlation matrix frames at eachpredetermined point in time are added to generate a two-dimensionalhemodynamic map indicative of the strength of the spontaneoushemodynamic oscillations to assess the viability of tissue in thepredetermined area or assess the viability of other hemodynamicparameters, step 176.

The result is system 10 and the method thereof provides a contactlessreal-time assessment of tissue viability and other hemodynamicparameters that allows a user to quantitatively assess the tissue healthto provide objective metrics to support and guide accurate tissueexcision of a burn wound or similar type wound. System 10 and the methodthereof allows clinicians to selecting a level of debridement of a burnwound at a desired depth to minimize inflammation and determine theoptimal treatment and remove virtually all the necrotic tissue in theburn wound or similar type wound in a time efficient manner. System 10and the method thereof eliminates the need for intrusive tissue contactand preferably provides for long distance tissue viability assessmentmonitoring when compared to more conventional invasive imaging systemsand methods discussed in the Background section. System 10 and themethod thereof may provide opportunities in settings wheremulti-individual assessment may be extremely difficult or not feasible,such as intensive care units, emergency rooms, or where the condition ofthe patient may not allow for contact measurements.

One advantage of system 10 and the method thereof relying on spontaneoushemodynamic oscillation measurements discussed above with reference toone or more of FIG. 1-6, rather than absolute concentration measurementsof chromophores present in the cardiovascular system, is an optical pathlength factor approximation is not required by system 10 and the methodthereof. This may eliminate the need to rely on estimation errors.System 10 and method thereof, unlike conventional near infraredspectroscopy (NIRS) techniques, preferably does not require absoluteconcentration retrieval of the chromophores present in thecardiovascular system of tissue 16 of predetermined area 18 of humansubject 16. Instead, system 10 and the method thereof preferablyutilizes controller 50, one or more light sources 12, and one or moredetectors 20. In one example.

For enablement purposes only, the following code portions are providedwhich can be executed on one or more processor, a computing device, orcomputer to carry out the primary steps and/or functions of contactlesssystem 10 and method for assessing tissue viability and otherhemodynamic parameters discussed above with reference to one or more ofFIGS. 1-6 . Other equivalent algorithms and code can be designed by asoftware engineer and/or programmer skilled in the art using theinformation provided herein.

%Acquire image Frame = get frame (n,m) from camera/sensors etc.%Determine ROI (region of interest) maskmother = zeros(n,m) %set to zeroa matrix equal to the size of the acquired image % Set to 1 an area ofinterest where reference signal will be calculated from mask_1 = ones(maskmother (n,m) ) %Average pixels within selected ROI: im = Frame.*mask_1 %Detrend im signal im = im − im_Trend %identify frequencycomponents in im signal by FFT (Fast Fourier Transform) PSD = FFT (im)%Extrapolate Reference Signal by performing Inverse Fourier Transformonly between frequency range of interest (for example HR, respirationrate etc.). Discard imaginary part Ref = Real [FFT⁻¹( PSD(C1<f<C2) )]%Integrate reference signal and acquired images product over time toobtain hemodynamic map (S): S = sum_(t) (Ref.*Frame)

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicantscannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is:
 1. A contactless system for assessing tissueviability and other hemodynamic parameters, the system comprising: oneor more light sources configured to emit lights at a predeterminedwavelength sensitive to hemoglobin concentration associated withspontaneous hemodynamic oscillations at tissue in a predetermined areaof a human subject; one or more polarizers each coupled to one or moreof the one or more light sources configured to polarize the light to apolarized state such that the polarized light in the polarized statediffuses into the tissue in the predetermined area at a predetermineddepth and the polarized light is maintained in the polarized state atthe predetermined depth; one or more detectors each including a detectorpolarizer coupled thereto configured to discriminate the lightmaintained in the polarized state and at the predetermined depth andconfigured to generate a plurality of frames of the tissue in thepredetermined area at the predetermined depth; and a controller coupledto the one or more light sources and the one or more detectors, thecontroller configured to: acquire the plurality of frames, select aregion of interest having the same coordinates for each of the pluralityof frames, average the number of pixels within each region of interestto create a raw reference signal, detrend the raw reference signal tocreate a detrended raw reference signal, perform frequency domainanalysis of the detrended raw reference signal, identify a frequencyband of interest associated with the spontaneous hemodynamicoscillations, perform an inverse fast Fourier transform within thefrequency band of interest to generate a reference signal including aplurality of samples and indicative of blood volume oscillations at aselected spontaneous hemodynamic oscillation, for each sample of thereference signal at a predetermined point in time, multiply the sampleby each pixel of a frame at the same predetermined point in time togenerate a three-dimensional coordinate matrix including a plurality ofcorrelation matrix frames at each predetermined point in time, and addthe plurality of correlation matrix frames at each predetermined pointin time to generate a two-dimensional hemodynamic map indicative of thestrength of the spontaneous hemodynamic oscillation to assess theviability of the tissue and/or the other hemodynamic parameters in thepredetermined area.
 2. The system of claim 1 in which the spontaneoushemodynamic oscillations have a frequency in the range of 0.05 Hz toabout 1.5 Hz.
 3. The system of claim 1 in which the predeterminedwavelength is in the range of about 500 nm to about 1,000 nm.
 4. Thesystem of claim 1 in which the predetermined depth is in the range ofabout 0.1 mm to about 0.5 mm.
 5. The system of claim 1 in which theother hemodynamic parameters include one or more of: heart rate, restingheart rate, heart rate variability, and tissue saturation for patientssuffering from diminished blood circulation.
 6. The system of claim 1 inwhich the one or more detectors include a CCD camera.
 7. The system ofclaim 1 in which the one or more detectors include a CMOS camera.
 8. Thesystem of claim 1 in which the predetermined area includes a burn areaof the human subject.
 9. The system of claim 1 in which thepredetermined area includes a wound area of a human subject.
 10. Thesystem of claim 1 further including a light filtering lens coupled toone or more light sources.
 11. A contactless method for assessing tissueviability and other hemodynamic parameters, the method comprising:emitting light at a predetermined wavelength sensitive to hemoglobinconcentration associated with spontaneous hemodynamic oscillations attissue in a predetermined area of a human subject; polarizing the lightto a polarized state such that the polarized light in the polarizedstate diffuses into the tissue in the predetermined area at apredetermined depth and the polarized light is maintained in thepolarized state at the polarized depth; discriminating the lightmaintained in the polarized state and at the predetermined depth andgenerating a plurality of frames of the tissue in the predetermined areaat the predetermined depth; acquiring the plurality of frames; selectinga region of interest having the same coordinates for each of theplurality of frames; averaging the number of pixels within each regionof interest to create a raw reference signal; detrending the rawreference signal to create a detrended raw reference signal; performingfrequency domain analysis of the detrended raw reference signal;identifying a frequency band of interest associated with the spontaneoushemodynamic oscillations; performing an inverse fast Fourier transformwithin the frequency band of interest to generate a reference signalincluding a plurality of samples and indicative of blood volumeoscillations at a selected spontaneous hemodynamic oscillation; for eachsample of the reference signal at a predetermined point in time,multiplying the sample by each pixel of a frame at the samepredetermined point in time to generate a three-dimensional coordinatematrix including a plurality of correlation matrix frames at eachpredetermined point in time; and adding the plurality of correlationmatrix frames at each predetermined point in time to generate atwo-dimensional hemodynamic map indicative of the strength of thespontaneous hemodynamic oscillation to assess the viability of thetissue and/or the other hemodynamic parameters in the predeterminedarea.
 12. The method of claim 11 in which adding the plurality ofcorrelation matrix frames at each predetermined point in time togenerate a two-dimensional hemodynamic map indicative of the strength ofthe spontaneous hemodynamic oscillation assess the viability of otherhemodynamic parameters including one or more of: heart rate, restingheart rate, heart rate variability, and tissue saturation for patientssuffering from diminished blood circulation.
 13. The method of claim 11in which the spontaneous hemodynamic oscillations have a frequency inthe range of 0.05 Hz to about 1.5 Hz.
 14. The method of claim 11 inwhich the predetermined wavelength is in the range of about 500 nm toabout 1,000 nm.
 15. The method of claim 11 in which the predetermineddepth is in the range of about 0.1 mm to about 0.5 mm.
 16. The method ofclaim 11 in which the predetermined area includes a burn area of thehuman subject.
 17. The method of claim 11 in which the predeterminedarea includes a wound area of a human subject.
 18. A contactless systemfor assessing tissue viability and other hemodynamic parameters, thesystem comprising: one or more light sources configured to emit lightsat a predetermined wavelength sensitive to hemoglobin concentrationassociated with spontaneous hemodynamic oscillations into tissue at apredetermined area of a human subject; one or more polarizers eachcoupled to one or more of the one or more light sources configured topolarize the light to a polarized state such that the polarized light inthe polarized state diffuses into the tissue in the predetermined areaat a predetermined depth range and the polarized light is maintained inthe polarized state at the predetermined depth range; one or moredetectors each including a detector polarizer coupled thereto configuredto discriminate the light maintained in the polarized state and at thepredetermined depth range from polarized light reflected from the tissuein the predetermined area which has not been maintained in the polarizedstate and configured to generate a plurality of frames of the tissue inthe predetermined area at the predetermined depth; and a controllercoupled to the one or more light sources and the one or more detectorsconfigured to acquire the plurality of frames and configured to assessthe viability of the tissue and/or the other hemodynamic parameters inthe predetermined area using the discriminated light maintained in thepolarized state and at the predetermined depth range.
 19. The system ofclaim 18 in which the controller is configured to generate atwo-dimensional hemodynamic map indicative of the strength of thespontaneous hemodynamic oscillation to further assess the viability ofthe tissue and/or the other hemodynamic parameters.
 20. The system ofclaim 18 in which the controller is configured to perform one or more orall of the following: select a region of interest having the samecoordinates for each of the plurality of frames; average the number ofpixels within each region of interest to create a raw reference signal;detrend the raw reference signal to create a detrended raw referencesignal; perform frequency domain analysis of the detrended raw referencesignal; identify a frequency band of interest associated with thespontaneous hemodynamic oscillation; perform an inverse fast Fouriertransform within the frequency band of interest to generate a referencesignal including a plurality of samples and indicative of blood volumeoscillations at a selected spontaneous hemodynamic oscillation; for eachsample of the reference signal at a predetermined point in time,multiply the sample by each pixel of a frame at the same predeterminedpoint in time to generate a three-dimensional coordinate matrixincluding a plurality of correlation matrix frames at each predeterminedpoint in time; and add the plurality of correlation matrix frames ateach predetermined point in time to generate a two-dimensionalhemodynamic map indicative of the strength of the spontaneoushemodynamic oscillation to assess the viability of the tissue and/or theother hemodynamic parameters in the predetermined area.
 21. The systemof claim 18 in which the spontaneous hemodynamic oscillations have afrequency in the range of 0.05 Hz to about 1.5 Hz.
 22. The system ofclaim 18 in which the predetermined wavelength is in the range of about500 nm to about 1,000 nm.
 23. The system of claim 18 in which thepredetermined depth is in the range of about 0.1 mm to about 0.5 mm. 24.The system of claim 18 in which the other hemodynamic parameters includeone or more of: heart rate, resting heart rate, heart rate variability,and tissue saturation for patients suffering from diminished bloodcirculation.
 25. The system of claim 18 in which the one or moredetectors include a CCD camera.
 26. The system of claim 18 in which theone or more detectors include a CMOS camera.
 27. The system of claim 18in which the predetermined area includes a burn area of the humansubject.
 28. The system of claim 18 in which the predetermined areaincludes a wound area of a human subject.
 29. The system of claim 18further including a light filtering lens coupled to one or more lightsources.
 30. A contactless method for assessing tissue viability andother hemodynamic parameters, the method comprising: emitting light at apredetermined wavelength sensitive to hemoglobin concentrationassociated with spontaneous hemodynamic oscillations into tissue at apredetermined area of a human subject; polarizing the light to apolarized state such that the polarized light in the polarized statediffuses into the tissue in the predetermined area at a predetermineddepth range and the polarized light is maintained in the polarized stateat the polarized depth range; discriminating the light maintained in thepolarized state and at the predetermined depth range from polarizedlight reflected from the tissue in the predetermined area which has notbeen maintained in the polarized state and generating a plurality offrames of the tissue in the predetermined area at the predetermineddepth range; and acquiring the plurality of frames to assess theviability of the tissue and/or the other hemodynamic parameters in thepredetermined area using the discriminated light maintained in thepolarized state and at the predetermined depth range.
 31. The method ofclaim 30 further including generating a two-dimensional hemodynamic mapindicative of the strength of the spontaneous hemodynamic oscillation tofurther assess the viability of the tissue and/or the other hemodynamicparameters in the predetermined area.
 32. The method of claim 30 furtherincluding performing one or more or all of the following: acquiring theplurality of frames; selecting a region of interest having the samecoordinates for each of the plurality of frames; averaging the number ofpixels within each region of interest to create a raw reference signal;detrending the raw reference signal to create a detrended raw referencesignal; performing frequency domain analysis of the detrended rawreference signal; identifying a frequency band of interest associatedwith the spontaneous hemodynamic oscillations; performing an inversefast Fourier transform within the frequency band of interest to generatea reference signal including a plurality of samples and indicative ofblood volume oscillations at a selected spontaneous hemodynamicoscillation; for each sample of the reference signal at a predeterminedpoint in time, multiplying the sample by each pixel of a frame at thesame predetermined point in time to generate a three-dimensionalcoordinate matrix including a plurality of correlation matrix frames ateach predetermined point in time; and/or adding the plurality ofcorrelation matrix frames at each predetermined point in time togenerate a two-dimensional hemodynamic map indicative of the strength ofthe spontaneous hemodynamic oscillation to assess the viability of thetissue and/or the other hemodynamic parameters in the predeterminedarea.
 33. The method of claim 30 in which the other hemodynamicparameters include one or more of: heart rate, resting heart rate, heartrate variability, and tissue saturation for patients suffering fromdiminished blood circulation.
 34. The method of claim 30 in which thespontaneous hemodynamic oscillations have a frequency in the range of0.05 Hz to about 1.5 Hz.
 35. The method of claim 30 in which thepredetermined wavelength is in the range of about 500 nm to about 1,000nm.
 36. The method of claim 30 in which the predetermined depth is inthe range of about 0.1 mm to about 0.5 mm.
 37. The method of claim 30 inwhich the predetermined area includes a burn area of the human subject.38. The method of claim 30 in which the predetermined area includes awound area of a human subject.